The essential requisites of life for all life forms (light, heat, water, food, and habitats) are supplied by the biosphere. Biosphere is very complex and large, so it is divided into smaller units (ecosystems). Each ecosystem consists of two parts: biotic and abiotic. Biotic category is subdivided into 3 functional groups: 1) producers: the autotrophic (self-nourishing) organisms (green plants and algae) 2) consumers: the heterotrophic organisms (all animal life) 3) Decomposers: heterotrophic organisms like bacteria and fungi that break down waste materials (including dead producers and consumers) to again make chemical components available to producers. The largest and most commonly studied phyla of animals are: 1 2 3 4 5 6 7 8 Porifera (sponges) Cnidaria (jellyfish, hydras, sea anemones, Portuguese man-of-wars, and corals) Platyhelminthes (flatworms, including planaria, flukes, and tapeworms) Nematoda (roundworms, including rotifers and nematodes) Mollusca (mollusks, including bivalves, snails and slugs, and octopuses and squids) Annelida (segmented worms, including earthworms, leeches, and marine worms) Echinodermata (including sea stars, sea cucumbers, sand dollars, and sea urchins) Arthropods (including arachnids, crustaceans, millipedes, centipedes, and
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insects) 9 Chordata (animals with nerve chords - this group includes the vertebrates)
Varieties of known species KINGDOM Bacteria Protoctists (algae, protozoa, etc) Animals, invertebrates Animals, vertebrates Birds Mammals Fungi Plants Total number of described species Estimated number of unknown species No. OF SPECIES 4,000 80,000 1,272,000 52,000 10,000 45000 72,000 270,000 1,750,000 14,000,000
[UNEP-WCMC (2000). Global Biodiversity: Earth's living resources in the 21st century. Cambridge, World Conservation Press.]
Chemical elements circulate between the organisms and the environment through pathways comprising the natural cycles: The hydrologic cycle The biogeochemical cycles: 1) carbon cycle 2) Nitrogen cycle 3) Phosphorus cycle 4) Sulfur cycle Biogeochemical cycle A biogeochemical cycle or nutrient cycle is a pathway by which a chemical element or molecule moves through both biotic (biosphere) and abiotic (lithosphere, atmosphere, and hydrosphere) compartments of Earth. In effect, the element is recycled, although in some cycles there may be places (called reservoirs) where the element is held for a long period of time (such as an ocean for water) Homeostatic mechanisms, called feedback loops, maintain the ecosystems in a stable condition. Now human activities are inducing large enough perturbations in the ecosystems which can permanently upset the balanced state of the natural cycles. Homeostatic Mechanism: definition Homeostatic mechanisms control a property of all living things called homeostasis. Homeostasis is a built-in, automated, and essential property of living systems. Breathing is an example of a homeostatic property. Homeostatic mechanisms are self-regulating mechanisms that function to keep a system in the steady state needed for survival. These mechanisms counteract the influences that drive physiological properties towards a more unbalanced state.
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The hydrologic cycle The water on which humans depend so heavily – lakes, streams, and ground water – accounts for less than 1% of total supply. Hydrologic cycle has two main reciprocal mechanisms – evaporation and precipitation. Most evaporation occurs over oceans. Each year, about 4,23,000 cubic km of water is evaporated.
Different Processes Precipitation Condensed water vapor that falls to the Earth's surface. Most precipitation occurs as rain, but also...